For the determination of the heavy nitrogen content of a given specimen, it has been customary to resort to a procedure which involves decomposing the specimen such as by the Kjeldahl method to determine the total nitrogen content of the specimen and thereafter determine the percentage of heavy nitrogen by mass spectrographic or spectroscopic analysis of the portion of nitrogen from the specimen which has been collected in the form of ammonium sulfate. In this procedure, however, when the amount of the specimen used is small, a potential for error in the measurement of the heavy nitrogen concentration is unacceptably increased since the ammonia present in the reagents and in the ambient air enters the reaction system in a relatively large quantity between the time when the specimen is decomposed and the time the nitrogen is recovered in the form of ammonium sulfate.
In recent years, a variety of methods have been developed for the spectroscopic measurement of heavy nitrogen concentration in specimens and analytical devices designed exclusively for such masurement have found widespread acceptance. Even where such a specific analytical device is used, it is necessary that determination of the total nitrogen content of the specimen be made independently and thereafter, determination of heavy nitrogen content of that specimen be effected by measuring the concentration of heavy nitrogen. In the prior art methods described above the determination of total nitrogen content of the specimen and the measurement of the concentration of heavy nitrogen are carried out by separate procedures totally different from each other and, therefore, of are unacceptably time-consuming where the test in question is to be performed on numerous specimens.